1. Field of the Invention
The present invention relates to a method of controlling a ram speed of a press ram of a metal-forming press, comprising the steps of superimposing a second drive energy from an auxiliary drive on a first drive energy from a main drive and driving the press ram at the resultant speed. The present ivnention additionally relates to a driving device for a press ram of a metal-forming press.
2. Description of the Invention
The prior art discloses a large number of solutions for determining a drive characteristic (speed profile) of the press ram of a metal-forming press during a total cycle (one stroke) of the press ram, said total cycle consisting of energy supply, acceleration of the press ram, stationary phase, energy recovery and metal-forming phase.
It is, for example, known to equip a press drive with two flywheels and the associated clutches and to adjust a desired speed profile of the press ram by alternately actuating said clutches. Such drives are, however, comparatively complicated and uneconomical as far as the energy consumed is concerned.
It is also known to use for press drives of metal-forming presses single-stage planetary gearings in the case of which two different output speeds of the gearing are provided via clutch/brake combinations.
For decelerating the press ram (negative acceleration) the energy that has to be removed from the drive when shifting to a lower speed is normally dissipated as lost energy towards the machine frame and converted into frictional energy (heat) which is not suitable for further use.
German Patent No. DE 40 24 290 discloses the measure of superimposing an auxiliary drive on a main drive so as to realize arbitrary speed profiles for the press ram. The moments of inertia which have to be overcome for introducing the auxiliary energy are, however, substantial.